Chemical Resistance of O-Ring Material

When an O-ring needs replacement (such as in a mechanical vacuum pump), the manufacturer can provide, or recommend, an O-ring that will be resistant to the pump s vacuum fluid. On the other hand, when an O-ring is being used in varying conditions, you will be responsible for the selection of the proper O-ring material to maintain the integrity of your system and the health and safety of the operators. 

As is typical for most polymers, the material composition of an O-ring may be suitable for one chemical environment and unsuitable for another. For example, ethylene propylene rubber is excellent in water conditions and exhibits essentially no swelling in these environments. However, if any lubrication is required, a petroleum-based lubricant will deteriorate the rubber. If needed, a silicone, glycerin, or ethylene glycol lubricant is recommended. 

An increase in size is a common reaction to O-ring materials in specific harsh environments. This is not necessarily bad if expansion enhances sealing. The worst that happens is that when the apparatus is taken apart, the O-ring is no 

There are seven primary materials from which O-rings are made. Table 1.9 catalogs these different materials, listing suitable and unsuitable chemical contacts and properties for each. Also included is a single O-ring price comparison (these 1991 prices are not meant to be absolute and are only offered to provide comparison). 

Incidentally, several companies cover one type of O-ring material (i.e., Buna-N) with a Teflon sheath. These O-rings have the resiliency of less expensive O-rings with the chemical inertness of Teflon. 

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